1. Field of the Invention
The present invention relates to a technology for scanning a target surface with a light beam.
2. Description of the Related Art
An image forming apparatus employing a laser is widely used in the field of electrophotographic image recording. Such an image forming apparatus typically includes an optical scanning device to form a latent image by rotating a photosensitive drum while scanning a laser beam in the axial direction of the drum using a deflector (e.g., a polygon mirror). In the field of electrophotography, the image forming apparatus needs to provide a high-density image to enhance the image quality and to achieve a fast image output to enhance the throughput.
A method of achieving both the high density and the fast image output includes a so-called multi-beam approach where a scanning is performed simultaneously with a plurality of light beams.
However, if a part of a light beam from a light source is reflected at an optical system and returns to the light source as a stray light, it may affect the optical intensity of the light beam from the light source. Furthermore, it is also possible that the stray light is reflected at the light source and incident on the optical system again, causing a density fluctuation in the image.
In view of these circumstances, an optical scanning device that reduces the stray light returning to the light source has been proposed (e.g., see Japanese Patent Application Laid-open No. 2006-259574, Japanese Patent Application Laid-open No. H7-113970, and Japanese Patent Application Laid-open No. 2007-25165).
In the optical scanning device disclosed in Japanese Patent Application Laid-open No. 2006-259574, however, there is a possibility that the spot sizes on a photosensitive element may vary if a light source having a plurality of light-emitting units is used. Furthermore, problems with the optical scanning devices disclosed in Japanese Patent Application Laid-open No. H7-113970 and Japanese Patent Application Laid-open No. 200725165 are that the cost may increase and the light utilization efficiency may decrease.